高精度运算之加减乘

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<queue>
using namespace std;
#define N 1100

void change(char s[], int a[])///把字符串类型的s转化成数字倒着存入a中；
{
    int j=0, len = strlen(s);
    for(int i=len-1; i>=0; i--)
    {
        a[j++] = s[i]-‘0‘;
    }
}
void Add(int a[], int b[], int sum[])
{
    for(int i=0; i<N-1; i++)
    {
        int m = sum[i]+a[i]+b[i];
        sum[i] = m%10;
        sum[i+1] += m/10;
    }
}
void Sub(int a[], int b[], int c[])
{
    for(int i=0; i<N; i++)
    {
        if(a[i]-b[i] < 0)///借位；
        {
            c[i] = a[i]+10-b[i];
            a[i+1] -= 1;
        }
        else
            c[i] = a[i] - b[i];
    }
}
void Mul(int a[], int b[], int c[])
{
    int m;
    for(int i=0; i<N; i++)
    {
        for(int j=0; i+j+1<N; j++)
        {
            m = a[i]*b[j];
            m+=c[i+j];
            c[i+j] = m%10;
            c[i+j+1] += m/10;
        }
    }
}
int main()
{
    int T, t=1, i, f, a[N], b[N], c[N];
    char s1[N], s2[N];
    scanf("%d", &T);
    while(T--)
    {
        memset(a, 0, sizeof(a));
        memset(b, 0, sizeof(b));
        memset(c, 0, sizeof(c));
        f  =0;
        scanf("%s%s", s1,s2);

        int len1 = strlen(s1);
        int len2 = strlen(s2);

       /* if(len1<len2)
        {
            f=1;
            swap(s1, s2);
        }
        else
        {
            if(strcmp(s1, s2)<0)
                f=1,
                swap(s1, s2);
        }*////在减法中要用到这个；
        change(s1, a);
        change(s2, b);

        /// Add(a, b, c);/// +
        /*Sub(a, b, c);/// -
        if(f == 1) printf("-"); */
        Mul(a, b, c);/// *
        for(i=N-1; i>0; i--)
        {
            if(c[i]!=0)
                break;
        }
        printf("Case %d:\n", t++);
        printf("%s * %s = ", s1, s2);
        for(int j=i; j>=0; j--)
            printf("%d", c[j]);
        printf("\n");
        if(T!=0)
            printf("\n");
    }
    return 0;
}